Ever since 2,4-D was used as the means of chemically removing weeds, a numerous number of herbicides have been developed, and the time required for removal of weeds has thereby been drastically reduced. Because of anxiety about environmental pollution etc. raised in recent years, there is increasing demand for high-safety herbicides free from environmental pollution.
The present inventors have studied for the elucidation of toxins produced by plant-pathogenic microorganisms in order to obtain a novel substance having a weed-killing activity. By searching for a substance having a weed-killing activity among physiologically active substances produced by microorganisms, there is the possibility of finding a substance completely different from a synthetic compound with respect to the skeleton and nature of action. These naturally occurring substances are generally liable to enzyme degradation and thus least likely to remain in the environment. Out of such substances, bialaphos is a practically applied example developed by Meiji Seika Co., Ltd.